Robot vacuum reports C4 and stops; cliff sensor or drop sensor error is indicated.

Safety: Power off the robot and keep it away from stairs while testing.

• Locate cliff sensors: On the underside front edge, identify the small dark windows (usually 4–6) that house the cliff sensors.
• Clean sensor windows: Use a soft, dry microfiber cloth to gently wipe each sensor window. For stubborn grime, lightly dampen the cloth with water (no chemicals) and dry immediately.
• Check for physical damage: Inspect the plastic windows for cracks or deep scratches that could interfere with the infrared beam.
• Test on flat, light-colored floor: Place the robot on a flat, non-reflective surface away from edges and start a cleaning cycle. Avoid dark carpets or glass floors during testing, as they can confuse sensors.
• Advanced check: If the error persists, remove the bottom cover and verify that the cliff sensor harness is firmly connected to the main board and that the sensor board is not loose.
• Component replacement: If one or more sensors are physically damaged or still misreading after cleaning, replace the cliff sensor board assembly with a compatible Dreame part.